1. Field of the Invention
The present invention relates to a joining method, specifically to a joining method for joining different types of members to each other, e.g., a metal member to a metal member, a metal member to a resin member, and a resin member to a resin member.
2. Description of Related Art
As a method for joining different types of members of a metal member, a resin member, and the like, for example, there have been known a method using an adhesive (e.g., Japanese Patent Application Publication No. 11-173356 (JP 11-173356 A)) and a method using a fastening member such as a rivet or a screw. However, the former method has a problem that it takes time to cure the adhesive, and a problem that adhesive strength could be decreased due to aged deterioration and the like of the adhesive. Further, the latter method has a problem that a product weight is increased due to the rivet, the screw, or the like, and a problem that it takes time and man-hours to fasten the rivet, the screw, or the like.
In order to deal with such a problem, Japanese Patent Application Publication No. 2008-162115 (JP 2008-162115 A) and Japanese Patent Application Publication No. 2008-213379 (JP 2008-213379 A) describe a technique to join a metal member to a resin member more reasonably without using the adhesive or the fastening member.
The joining method disclosed in JP 2008-162115 A is a method in which thermo plastic resin is injected on a surface of metal on which a fine porous hydroxyl-group containing film is formed, so that the metal is integrated with the thermo plastic resin via the film.
Further, the joining method described in JP 2008-213379 A is a method including: a base portion preparation step of preparing a metal base portion; a recessed portion forming step of, after the base portion preparation step, forming a recessed portion having an opening on at least part of a surface of the base member and having an internal space extending toward a lower side of at least part of a peripheral part of the opening so as to form an overhang; and a coating portion forming step of, after the recessed portion forming step, forming a coating portion made of resin and including a merging portion that fills the recessed portion, and a skin portion integrated with the merging portion and covering the surface of the base portion.
In the joining method described in JP 2008-162115 A, the thermo plastic resin is injected on the surface of the metal on which the fine porous hydroxyl-group containing film is formed, so that the metal is integrated with the thermo plastic resin via the film. Accordingly, due to an anchor effect and a chemical operation of the fine porous hydroxyl-group containing film, the metal can be integrated with the thermo plastic resin with sufficient joining strength. Further, such a hydroxyl-group containing film can be formed easily at a low cost without using hydrazine, by performing a hot-water process on the surface of the metal. Accordingly, it is possible to safely manufacture a complex in which the metal and the thermo plastic resin molded in desired shapes are formed integrally with each other, at low cost without any bad smell.
Further, in the joining method described in JP 2008-213379 A, the recessed portion having an overhang structure, and the merging portion entering the recessed portion to fill the recessed portion are formed in the base portion of the coating portion. Accordingly, an anchor effect is obtained by the recessed portion and the merging portion, so that a resisting force occurs due to the anchor effect and a contraction stress by thermal expansion and the like of the coating portion is restrained. As a result, the skin portion formed integrally with the merging portion makes close contact with the surface of the base portion, thereby making it possible to prevent detachment of the coating portion from the surface of the base portion.
However, in the joining method described in JP 2008-162115 A, after the fine porous hydroxyl-group containing film is formed on the surface of the metal, it is necessary to inject the thermo plastic resin onto the surface. This may cause such a problem that its manufacturing process becomes complicated and a manufacturing cost is increased.
Also, in the joining method described in JP 2008-213379 A, how to form the coating portion made of resin and including the merging portion that fills the recessed portion and the skin portion formed integrally with the merging portion so as to cover the surface of the base portion is not specified concretely, and how the merging portion is caused to enter the internal space of the recessed portion is not mentioned at all.